A filler head (or filling head) of this type is usually in the form of a chamber or hollow body, the upper face of which is open into a part of the bodywork of the vehicle, with the free end of the upwardly directed filling pipe being open into this chamber or hollow body, the arrangement being such that a filling nozzle of a forecourt filling pump can be introduced into the chamber or hollow body so that the fuel tank can be filled. The filling orifice for the filling pipe may be closed or obturated by a removable filler cap, with the exposed face of the filler head being itself, if desired, hidden by a hinged flap or trap set into the outside of the bodywork.
With a view to eliminating the removably filler cap, it has previously been proposed to provide a filler head of the type comprising a bowl-shaped body, the upper face of which has a filling orifice, the filler head having a shut-off valve which is mounted for pivoting movement with respect to the bowl-shaped body between a rest or closed position, towards which it is urged resiliently, and in which it closes (or obturates) the filling orifice, and a withdrawn or open position in which it lies within the bowl of the body, and in which the filling orifice is open. The valve is a flap valve which is moved into its withdrawn position during introduction of the filling nozzle into the filling orifice.
In one known design of this type of filling head, the shut-off valve, which is equipped with a simple return spring for biassing it to the closed or rest position, is not locked in that position; alternatively it is provided with locking means which require positive control to achieve locking; or else the opening of the valve depends on opening of the access flap or trap.
The use of a shut-off valve which has no locking means gives rise to a danger that pollutants may accidentally be introduced into the fuel tank. This is especially the case when, during washing of the vehicle, the access trap and the zone around the filling orifice are washed using a jet of high pressure water or vapour. The pressure employed can be sufficiently high to cause the shut-off valve to open accidentally.
When the shut-off valve is equipped with externally controlled locking means, its locking then depends on positive action being taken by the user. This solution is not entirely satisfactory because the user may forget to lock it.